Aluminum Phosphate or Polyphosphate Particles for Use as Pigments in Paints and Method of Making Same

ABSTRACT

An aluminum phosphate or polyphosphate-based pigment product is made by a process comprising contacting phosphoric acid with aluminum sulfate and an alkaline solution to produce an aluminum phosphate based product; and optionally calcining the aluminum phosphate based product at an elevated temperature, wherein the process is substantially free of an organic acid. The aluminum phosphate or polyphosphate-based pigment is amorphous. The amorphous aluminum phosphate or polyphosphate characterized by a bulk density of less than 2.30 grams per cubic centimeter and a phosphorus to aluminum mole ratio of greater than 0.8. The composition is useful in paints and as a substitute for titanium dioxide

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.11/215,312 filed Aug. 30, 2005, which claims priority to BrazilianPatent Application No. PI0403713-8, filed on Aug. 30, 2004, thedisclosures of which are incorporated by reference herein in theirentirety.

BACKGROUND

1. Field of the Invention

The invention relates to methods of making hollow particles of aluminumphosphate, aluminum orthophosphate and aluminum polyphosphate. Thisinvention further relates to use of such particles as pigments inpaints.

2. Background of the Invention

Titanium dioxide is the most common white pigment due to its strongability to backscatter visible light, which is in turn dependent on itsrefractive index. Substitutes for titanium dioxide have been sought, butthe refractive indexes of both the anatase and rutile forms of thisoxide are much higher than those of any other white powder, due tostructural reasons.

Titanium dioxide pigments are insoluble in coating vehicles in whichthey are dispersed. The performance properties of such titanium dioxidepigments, including its physical and chemical characteristics, aredetermined by the particle size of the pigment and the chemicalcomposition of its surface. Titanium dioxide is commercially availablein two crystal structures: anatase and rutile. Rutile titanium dioxidepigments are preferred as they scatter light more efficiently and aremore stable and durable than anatase pigments. Titanium dioxide scatterslight in two ways: refraction and detraction. The decorative andfunctional attributes of titanium dioxide, due to its refraction anddiffraction capabilities, make it a highly desirable pigment. However,titanium dioxide is known to be an expensive pigment to manufacture.Accordingly, there is a need for a more affordable substitute fortitanium dioxide as a pigment.

As mentioned, a desired feature of titanium dioxide is its largecapacity of spreading (or scattering) the visible light. This propertyis the result of its high refraction index, together with the absence ofelectronic transitions in the visible part of the spectrum. Manyattempts have been carried out to replace the titanium dioxide,partially or totally in its applications as pigment. However, therefraction indices of its two forms, anatase and rutile, are difficultto obtain by other white solid substances (Handbook of Chemistry andPhysics, CRC Press, 57th ed., 1983). Thus, the search for new whitepigments led to the search of systems with other light spreadingmechanism. Multiphase media, which present a large variation of therefraction index, may operate as light spreaders.

The current options for manufacturing processes of pigments or paintsthat result in a film containing “pores” in the internal part of theparticles or between the particles and the resin is also quite limited.Some techniques for hollow particle preparation have been described inthe literature, however, most techniques involve the manufacturing ofspheroidal hollow and polymeric particles by polymerization in emulsion.An example is the study of N. Kawahashi and E. Matijevic (Preparation ofHollow Spherical Particle of Itrium Compounds, J Colloid and InterfaceScience 143(1), 103, 1991) on the recovering of the polystyrene latexwith basic itrium carbonate and subsequent calcination in high airtemperatures, producing hollow particles of itrium compounds.

The preparation of hollow particles of aluminum metaphosphates bychemical reaction between the sodium metaphosphate and aluminum sulfate,followed by thermal treatment, was described by Galembeck et al. inBrazilian Patent BR 9104581. This study referred to the formation ofhollow particles of aluminum phosphate synthesized from sodium phosphateand aluminum nitrate. As mentioned, the two pigments, aluminum phosphateand metaphosphate, can be used to replace a large part of TiO₂ in paintsbased on PVA latex or acrylic emulsions.

Brazilian Patent BR 9500522-6 of Galembeck et al. describes a way ofmaking a white pigment from a double aluminum and calcium metaphosphate,obtained directly by a chemical reaction between the aluminummetaphosphate and calcium carbonate particles in a polymeric latexemulsion type aqueous medium. This patent extended the previous resultsto calcium salts that, from the environmental point of view, areadvantageous due to their full atoxicity.

Several publications discuss the synthesis of aluminum phosphatematerials primarily for use as a catalyst support including crystallineand amorphous forms. Many of these methods yield highly porous andcrystalline forms and few thermally stable amorphous compositions.Examples of such materials are described in U.S. Pat. Nos. 3,943,231;4,289,863; 5,030,431; 5,292,701; 5,496,529; 5,552,361; 5,698,758;5,707,442; 6,022,513; and 6,461,415. There exists a need, however, foraluminum phosphate with hollow particles, particularly for a powder thatcould be manufactured with relative ease.

SUMMARY OF THE INVENTION

The subject of this invention is the product and process of making anamorphous aluminum phosphate or polyphosphate characterized by a bulkdensity of between 1.95 and 2.30 grams per cubic centimeter and aphosphorus to aluminum mole ratio of greater than 0.8. The aluminumphosphate or polyphosphate may be in slurry form. Also, the aluminumphosphate or polyphosphate may be in powder form and, for example, haveone to four voids per particle of amorphous aluminum phosphate orpolyphosphate powder. The powder form of the product may comprise anaverage individual particle radius size of between 10 and 40 nanometers.The aluminum phosphate or polyphosphate may be used as an ingredient ina paint, and preferably, as a substitute (in part or in whole) fortitanium dioxide. The product may also be used as an ingredient in avarnish, printing ink, or plastic. The aluminum phosphate orpolyphosphate may be dried at temperatures below 130° C., and even atroom temperature, to produce a powder that contains 10-20 water weightpercent.

The amorphous aluminum phosphate or polyphosphate pigment may be made bycontacting phosphoric acid with aluminum sulfate and an alkalinesolution, either simultaneously or otherwise, and optionally calciningthe aluminum phosphate based product at an elevated temperature, whereinthe process is substantially free of an organic acid. The mixture has apH in the range from about 4.0 to about 4.5.

The process of making a the amorphous aluminum phosphate orpolyphosphate generally comprises the following steps: combiningphosphoric acid, aluminum sulfate, and sodium hydroxide into asuspension; filtrating and washing said suspension into a cake;dispersion of the washed cake; drying of the cake; polymerization of thedry product; and micronization of the product.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a transmission electron photomicrograph of a sample of theinventive material using 25 eV inelastic scattered electrons.

FIG. 2 is a bright field transmission electron micrograph of theinventive material.

FIG. 3 is a bright field transmission electron micrograph demonstrating“necking.”

DESCRIPTION OF EMBODIMENTS OF THE INVENTION

In the following description, all numbers disclosed herein areapproximate values, regardless whether the word “about” or “approximate”is used in connection therewith. They may vary by 1 percent, 2 percent,5 percent, or, sometimes, 10 to 20 percent. Whenever a numerical rangewith a lower limit, R^(L) and an upper limit, R^(U), is disclosed, anynumber falling within the range is specifically disclosed. Inparticular, the following numbers within the range are specificallydisclosed: R=R^(L)+k*(R^(U)−R^(L)), wherein k is a variable ranging from1 percent to 100 percent with a 1 percent increment, i.e., k is 1percent, 2 percent, 3 percent, 4 percent, 5 percent, . . . , 50 percent,51 percent, 52 percent, . . . , 95 percent, 96 percent, 97 percent, 98percent, 99 percent, or 100 percent. Moreover, any numerical rangedefined by two R numbers as defined in the above is also specificallydisclosed.

The invention described in this patent relates to non-crystallinesolids, as opposed to the large majority of inorganic industrialchemicals, including those products currently sold as crystallinealuminum phosphates or polyphosphates. The CAS number most often givenfor aluminum phosphate products is 7784-30-7, but this refers to astoichiometric, crystalline solid. There are not yet CAS numbersspecifically assigned to amorphous aluminum phosphates, following asearch in the ACS SciFinder® retrieval system.

Amorphous (i.e., non-crystalline) solids exhibit differences from theircrystalline counterparts with a similar composition, and suchdifferences may yield beneficial properties. For example, suchdifferences may include: (i) the non-crystalline solids do not diffractx-rays at sharply defined angles but may produce a broad scattering haloinstead; (ii) the non-crystalline solids do not have well definedstoichiometry, thus they can cover a broad range of chemicalcompositions; (iii) the variability of chemical composition includes thepossibility of incorporation of ionic constituents other than aluminumand phosphate ions; (iv) as amorphous solids are thermodynamicallymeta-stable, they may demonstrate a tendency to undergo spontaneousmorphological, chemical and structural changes; and (v) the chemicalcomposition of crystalline particle surface and bulk is highly uniformwhile the chemical composition of surface and bulk of amorphousparticles may show large or small differences, either abrupt or gradual.In addition, while particles of crystalline solids tend to grow by thewell-known mechanism of Ostwald ripening, non-crystalline particles mayexpand or swell and shrink (de-swell) by water sorption and desorption,forming a gel-like or plastic material that is easily deformed whensubjected to shearing, compression or capillary forces.

As mentioned, one aspect of the invention described herein is asynthetic process that produces non-crystalline aluminum phosphates withunique properties. When a dispersion of such particles dries under airat room temperature or up to 120° C., nanosized particles are formedthat have a core-and-shell structure. Such particles may be observed byanalytical electron microscopy. Moreover, these particles contain manyvoids dispersed as closed pores in their interior. The cores of theparticles are more plastic than the respective shells of the particles.This phenomenon is evidenced by growth of the voids upon heating, whilethe perimeter of the shells remains essentially unaltered.

Another aspect of the invention consists of the development of a newproduct and manufacturing process to form hollow particles of aluminumphosphate and polyphosphate to be used as a pigment. More specifically,this aspect of the invention relates to a new pigment obtained throughthe reaction of the phosphoric acid, particularly industrial-gradephosphoric acid, with aluminum sulfate under controlled pH andtemperature conditions. The reactant may be filtered, dispersed, dried,calcinated, and micronized for usage as pigment in paints, including inhouse acrylic paints. Such pigments may be used in other products andapplications, such as paints, plastics, varnishes, printing inks, etc.

As described herein, many have sought the formation of voids withinparticles, but it is a difficult objective to obtain because themajority of solids form open pores upon drying, and such open pores donot contribute to paint opacity or hiding power. The hollow particlesformed within aluminum phosphate or polyphosphate confer beneficialcharacteristics, both physically and chemically, that can be used inmany different applications. One aspect of the inventions describedherein is to produce aluminum phosphate or polyphosphate with suchhollow particles in order to take advantage of such beneficialcharacteristics.

The aluminum phosphate particles described herein demonstrate surprisingand unique properties. For example, the aluminum phosphate particlespresent voids, even when the particles are dried at room temperature, orup to 130 degrees Celsius. Preferably, the particles are dried between40 degrees Celsius and 130 degrees Celsius. More preferably, theparticles are dried between 60 degrees Celsius and 130 degrees Celsius.Even more preferably, the particles are dried between 80 degrees Celsiusand 120 degrees Celsius. In addition, the aluminum phosphate particleshave a core-and-shell structure. In other words, these particles haveshells chemically different from their cores. This property is evidencedby several different observations. First, the energy-filtered inelasticelectron images of the particles in the plasmon region (10-40 eV), asmeasured by a transmission electron microscope, show bright linessurrounding most particles. The contrast seen in plasmon micrographsdepends on local chemical composition, and in this regard, acore-and-shell particle structure can be observed from an examination ofthe micrograph in FIG. 1.

Next, the presence of voids within particles, as demonstrated in FIG. 2,dried at rather low temperatures are due to the fact that the particleslose weight by de-swelling, while their skins do not undergocontraction. Such voids, or hollow particles, are made possible if theplasticity of the particle core is higher than that of the shell.Additional indications of the formation of the hollow particles areobserved by heating the particles by concentrating the electron beam onthe particles. Large voids are then created within the particles, whiletheir perimeter undergoes little change. Even further indication of thepresence of closed voids, or hollow particles, is the bulk density ofaluminum phosphate prepared by the process described herein, which is inthe 1.95-2.27 g/cm³ range when measured at a water content ofapproximately 15-17%, as compared to the 2.5-2.8 g/cm³ values recordedfor aluminum phosphate dense particles. Preferably, the bulk density isless than 2.50 g/cm³. More preferably, the bulk density is less than2.30 g/cm³. More preferably, the bulk density is less than 2.10 g/cm³.More preferably yet, the bulk density is less than 1.99 g/cm³.

The aluminum phosphate particles, as prepared according to the processdescribed herein, may be dispersed in latex in the presence ofcrystalline particulate solids. If a film is cast using this dispersion,highly opaque films are produced. The highly opaque films are producedeven in the case of thin single layers of particles. Experimentalevidence for film opacity is obtained by using amorphous aluminumphosphate as a replacement for titanium dioxide (i.e., TiO₂). Titaniumdioxide is the current standard white pigment used by almost allmanufacturers involved in latex paint formulations. A standardstyrene-acrylic latex paint was prepared using a usual load of titaniumdioxide and it was compared to a paint wherein fifty percent of thetitanium dioxide load was replaced by amorphous aluminum phosphate. Thiscomparison was made in two different paint-testing laboratories. Theoptical measurements taken from films drawn using the two paintsdemonstrate that aluminum phosphate may replace titanium dioxideproducing films while preserving the optical properties of the film.

The surprising results and high effectiveness of the novel aluminumphosphate discussed herein is related in part to its relatively smallparticle size. Such smaller particle sizes allow the particles todistribute extensively in the film and to associate intimately with theresin and with inorganic paint fillers, thereby creating clusters thatare sites for extensive void formation when the paint dries. The presentaluminum phosphate shows this tendency to form closed voids, or hollowparticles, to an extent that has not been previously observed foraluminum phosphates, polyphosphates or any other particles. In someembodiments, the particles of aluminum phosphate or polyphosphate aresubstantially free of open pores while containing a number of closedpores. As a result, in such embodiments, the macropore volume issubstantially less than 0.1 cc/gram.

Opacification of water-based paint films using aluminum phosphate insome embodiments of the invention involves unique features. The wetcoating film is a viscous dispersion of polymer, aluminum phosphate,titanium dioxide and filler particles. When this dispersion is cast as afilm and dried, it behaves differently from a standard paint (below thecritical pigment volume concentration, CPVC). In a standard paint, thelow glass transition temperature (Tg) resin is plastic at roomtemperature and coalesced, so that the resin film fills pores and voids.A paint formulated with aluminum phosphate, however, can exhibit adifferent behavior. The closed pores form, as described herein, andcontribute to the film hiding power.

The effectiveness of the aluminum phosphate or polyphosphate describedherein can be compared to the particles of aluminum phosphate preparedby Hem et al. (see FIG. 3). The dry particles described therein do notshow small voids. In addition, the particles undergo large morphologicalchanges upon heating. The extensive formation of “necks,” as observed inthe work of Hem et al., is particularly interesting. Such necks are anindication that the particle surfaces are very deformable, as opposed torigid particles that demonstrate the beneficial properties provided bythe invention described herein.

The aluminum phosphate or polyphosphate in pigments can be prepared andused in at least one of the following forms: as a slurry pulp(dispersion of high content of solids, which flows under the action ofgravity or low pressure pumps) with 50% or more of solids; as dried andmicronized aluminum phosphate with 15% of humidity; and also in thepolymeric form as calcinated and micronized aluminum polyphosphate. Thealuminum phosphate or aluminum polyphosphate, used as a white pigment,can replace titanium dioxide in dispersions in aqueous medium, such aspolymeric latex emulsion. The phosphorus:aluminum molar ratio of thealuminum phosphate is preferably between 0.6 and 2.5. More preferably,the phosphorus:aluminum molar ratio of the aluminum phosphate is in therange of between 0.8 and 2.3. More preferably yet, thephosphorus:aluminum molar ratio of the aluminum phosphate is in therange of between 0.8 to 1.2.

As discussed, an aspect of the invention is a novel process ofmanufacturing hollow particles of aluminum phosphate or aluminumpolyphosphate that may be used in different applications, includingwhite pigment in the formulations of paints based on aqueous polymericlatex. The process is described in the following general steps. One ofskill in the art will recognize that certain steps may be altered oromitted altogether. The steps include: preparation of the main reagentsused in the process, such as diluted solution of phosphoric acid,diluted solution of aluminum sulfate, and diluted solution of sodiumhydroxide or ammonium hydroxide; simultaneous and controlled addition ofthe reagents in a reactor equipped with a sloshing system to keep thehomogeneity of the mixture during the process; control, during theaddition of the reagents in the reactor, of the temperature and pH(acidity) of the mixture and, mainly, the reaction time; filtration ofthe suspension, with approximately 8.0% of solids and separation of theliquid and solid phases, in an appropriate equipment; washing out of theimpurities present in the filter cake with slightly alkaline aqueoussolution; dispersion of the washed cake, containing approximately 35% ofthe solids, in an adequate disperser; drying of the dispersed pulp in aturbo-dryer; micronization of the dried product to an averagegranulometry of 5.0 to 10 microns; and polymerization of the driedproduct by thermal treatment of the aluminum phosphate in a calcinator.

There are several ways to prepare the main reagents in this process. Asmentioned, one source of phosphorus for the manufacturing of aluminumphosphate and of the aluminum polyphosphate is the fertilizer gradephosphoric acid, from any origin, as it is clarified and discolored. Forexample, a commercial phosphoric acid containing approximately 54% ofP₂O₅ ay be chemically treated and/or diluted with treated waterresulting in a concentration of 20% P₂O₅. Also, as an alternative tothis process (instead of fertilizer grade phosphoric acid or purifiedphosphoric acid), salts of phosphorus as orthophosphates or aspolyphosphates can be used.

Another reagent for the process is the commercial aluminum sulfate. Thealuminum sulfate may be obtained from the reaction between the alumina(hydrate aluminum oxide) with concentrated sulfuric acid (98% H₂SO₄),and then clarified and stored at a 28% concentration of Al₂O₃. For thereaction to have a favorable kinetics, the aluminum sulfate is dilutedwith water treated at 5.0% of Al₂O₃. As an alternative for this process,the source of aluminum can be any other salt of aluminum, as well asaluminum hydroxide or aluminum in metallic form.

The neutralization of the reaction is carried out with a sodiumhydroxide solution, which may be commercially purchased in differentconcentrations. A concentration of 50% of NaOH may be purchased anddiluted. For example, in the first phase of the reaction, when theinitial reagents are being mixed, the sodium hydroxide may be used inthe concentration of 20% of NaOH. In the second phase of the reaction,due to the need of a fine-tuning of the product acidity, a sodiumhydroxide solution with 5.0% of NaOH may be used. As an alternativeneutralizer, ammonium hydroxide or sodium carbonate (soda ash) may beused.

In one embodiment of the invention, a chemical reaction results in theformation of aluminum orthophosphate or of aluminum orthophosphates(Al₂(HPO₄)₃ or Al(H₂PO₄)₃. The reaction, as described, is carried outthrough the mixture of the three reagents, i.e., phosphoric acidsolution, aluminum sulfate solution, and sodium hydroxide solution. Thereagents are dosed in a reactor, typically containing a sloshing system,during a 30-minute period. During the addition of the reagents in thereactor, the pH of the mixture is controlled within a 4.0 to 4.5 rangeand a reaction temperature, between 35° C. and 40° C. The reaction iscompleted after 15 minutes of the reagent mixture. In this period, thepH of the mixture may be adjusted at 5.0, with the addition of morediluted sodium hydroxide. In this embodiment, the temperature ispreferably below approximately 40° C. At the end of the reaction, thesuspension formed should contain a molar relation between thephosphorus:aluminum elements in a 0.8 to 1.2 range.

After the formation of the aluminum orthophosphate, the suspensioncontaining around 6.0% to 10.0% of solids, with a maximum approximatetemperature of 45° C., and density in a 1.15 to 1.25 g/cm³ range, ispumped to a conventional filter press. In the filter press, the liquidphase (sometimes referred to as the “liquor”) is separated from thesolid phase (sometimes referred to as the “cake”). The wet cake,containing approximately 35% to 45% of solids, and still possiblycontaminated with the sodium sulfate solution, is kept in the filter forwashing cycle. The filtered concentrate, which is basically aconcentrated solution of sodium sulfate, is extracted from the filterand stored for future usage.

In one embodiment of the invention, the washing of the wet cake isperformed in the filter itself and in three process steps. In the firstwashing (“displacement washing”) the largest part of the filteredsubstance that is contaminating the cake is removed. The washing step isperformed using treated water over the cake at a flow rate of 6.0 m³ ofwater/ton of dried cake. A second washing step, also with treated waterand with a flow of 8.0 m³ of water/ton of dried cake, may be carried outto further reduce, if not eliminate, the contaminants. And, finally, athird washing step using a slightly alkaline solution may be carriedout. Such third washing step may be performed for the neutralization ofthe cake and to keep its pH in the 7.0 range. Finally, the cake may beblown with compressed air during a certain period of time. Preferably,the wet product should present between 35% and 45% of solids.

Next, in this particular embodiment of the invention, the cakedispersion may be processed in such a way that the filter cake, wet andwashed, and containing approximately 35% of solids, is extracted fromthe press filter by a conveyor belt and transferred to areactor/disperser. The dispersion of the cake is aided by the additionof a dilute solution of sodium tetrapyrophosphate.

After the dispersion step, the product is then dried, when the aluminumphosphate “mud,” with a percentage of solids within the 30% to 50%range, is pumped to the drying unit. In one embodiment, the waterremoval from the material can be carried out with drying equipment, suchas a “turbo dryer” type through an injection of a hot air stream, at atemperature of 135° C. to 140° C., through the sample. The finalhumidity of the product should preferentially be kept in the 10% to 20%of water range.

In certain embodiments of the invention, the next step of the processwould include product calcination. In this step, the orthophosphate ofthe dry aluminum, as Al(H₂PO₄)₃, is condensed by a thermal treatment toform a porous aluminum polyphosphate, that is (Al(H₂PO₄)₃)_(n), where“n” can be any integer greater than 1, preferably, n is greater than orequal to 4. More preferably, n is greater than or equal to 10. Even morepreferably, n is greater than or equal to 20. Preferably, n is less than100. Even more preferably, n is less than 50. This process step iscarried out by heating the phosphate aluminum, in a spray-drier typecalcinator, in a temperature range of 500° C. to 600° C. After thepolymerization, the product may be cooled quickly and sent to themicronization unit. At this point, product micronization step may becarried out. Finally, the resulting product that leaves the drier (orthe calcinator) is transferred to the grinding and finishing unit,ground in a micronizer/sorter, and its granulometry kept in the 99.5%range below 400 mesh.

The aluminum phosphate or the aluminum polyphosphate, after the thermaltreatment, can be applied as white pigment in the formulation of homepaints, based on water, due to its self-opacification property in latex,PVA, and acrylic films, due to the formation of particles with hollowstructures with high light spreading capacity, during the paint dryingprocess.

Various paints can be formulated using the aluminum phosphate orpolyphosphate made according to various embodiments of the invention asa pigment, alone or in combination with another pigment, such astitanium dioxide. A paint comprises one or more pigments and one or morepolymers as the binder (sometimes referred to as “binding polymer”), andoptionally various additives. There are water-borne paints andnon-water-borne paints. Generally, a water-borne paint composition iscomposed of four basic components: binder, aqueous carrier, pigment(s)and additive(s). The binder is a nonvolatile resinous material that isdispersed in the aqueous carrier to form a latex. When the aqueouscarrier evaporates, the binder forms a paint film that binds togetherthe pigment particles and other non-volatile components of thewater-borne paint composition. Water-borne paint compositions can beformulated according to the methods and components disclosed in U.S.Pat. No. 6,646,058, with or without modifications. The disclosure ofsuch patent is incorporated by reference in its entirety herein. Thealuminum phosphate or polyphosphate made according to variousembodiments of the invention can be used to formulate water-borne paintsas a pigment, alone or in combination with titanium dioxide.

A common paint is latex paints which comprises a binding polymer, ahiding pigment, and optionally a thickener and other additives. Again,the aluminum phosphate or polyphosphate made according to variousembodiments of the invention can be used to formulate latex paints as apigment, alone or in combination with dioxide. Other components formaking a latex paint is disclosed in U.S. Pat. No. 6,881,782 and U.S.Pat. No. 4,782,109, which are incorporated by reference herein in itsentirety. By way of illustration, suitable components and methods formaking latex paints are briefly explained below.

In some embodiments, suitable binding polymers include emulsioncopolymerized ethylenically unsaturated monomers including 0.8% to 6% offatty acid acrylate or methacrylate such as lauryl methacrylate and/orstearyl methacrylate. Based on the weight of copolymerized ethylenicmonomers, the polymeric binder comprises 0.8% to 6% fatty acidmethacrylate or acrylate where preferred compositions contain 1% to 5%of copolymerized fatty acid acrylate or methacrylate having an aliphaticfatty acid chain comprising between 10 and 22 carbon atoms. Preferredcopolymer compositions are based on copolymerized fatty acidmethacrylate. Lauryl methacrylate and/or stearyl methacrylate arepreferred and lauryl methacrylate is the most preferred monomer. Otheruseful fatty acid methacrylates include myristyl methacrylate, decylmethacrylate, palmitic methacrylate, oleic methacrylate, hexadecylmethacrylate, cetyl methacrylate and eicosyl methacrylate, and similarstraight chain aliphatic methacrylate. Fatty acid methacrylates oracrylates typically comprise commercial fatty oils coreacted withmethacrylic acid or acrylic acid to provide primarily the dominant fattyacid moiety methacrylate with minor amounts of other fatty acidacrylates or methacrylates.

Polymerizable ethylenically unsaturated monomers containcarbon-to-carbon unsaturation and include vinyl monomers, acrylicmonomers, allylic monomers, acrylamide monomers, and mono- anddicarboxylic unsaturated acids. Vinyl esters include vinyl acetate,vinyl propionate, vinyl butyrates, vinyl benzoates, vinyl isopropylacetates and similar vinyl esters; vinyl halides include vinyl chloride,vinyl fluoride, and vinylidene chloride; vinyl aromatic hydrocarbonsinclude styrene, methyl styrenes and similar lower alkyl styrenes,chlorostyrene, vinyl toluene, vinyl naphthalene, and divinyl benzene;vinyl aliphatic hydrocarbon monomers include alpha olefins such asethylene, propylene, isobutylene, and cyclohexene as well as conjugateddienes such as 1,3-butadiene, methyl-2-butadiene, 1,3-piperylene, 2,3dimethyl butadiene, isoprene, cyclohexane, cyclopentadiene, anddicyclopentadiene. Vinyl alkyl ethers include methyl vinyl ether,isopropyl vinyl ether, n-butyl vinyl ether, and isobutyl vinyl ether.Acrylic monomers include monomers such as lower alkyl esters of acrylicor methacrylic acid having an alkyl ester portion containing between 1to 12 carbon atoms as well as aromatic derivatives of acrylic andmethacrylic acid. Useful acrylic monomers include, for example, acrylicand methacrylic acid, methyl acrylate and methacrylate, ethyl acrylateand methacrylate, butyl acrylate and methacrylate, propyl acrylate andmethacrylate, 2-ethyl hexyl acrylate and methacrylate, cyclohexylacrylate and methacrylate, decyl acrylate and methacrylate,isodecylacrylate and methacrylate, benzyl acrylate and methacrylate, andvarious reaction products such as butyl phenyl, and cresyl glycidylethers reacted with acrylic and methacrylic acids, hydroxyl alkylacrylates and methacrylates such as hydroxyethyl and hydroxypropylacrylates and methacrylates, as well as amino acrylates andmethacrylates. Acrylic monomers can include very minor amounts ofacrylic acids including acrylic and methacrylic acid, ethacrylic acid,alpha-chloroacrylic acid, alpha-cyanoacrylic acid, crotonic acid,beta-acryloxy propionic acid, and beta-styryl acrylic acid.

In other embodiments, polymers useful as component (a), the “bindingpolymer”, of the latex paints are copolymerization products of a mixtureof co-monomers which comprise monomers selected from styrene, methylstyrene, vinyl, or combinations thereof. Preferably co-monomers comprise(more preferably consist essentially of) at least 40 mole percent ofmonomers selected from styrene, methyl styrene, or combinations thereofand at least 10 mole percent of one or more monomers selected fromacrylates, methacrylates, and acrylonitrile. Preferably, the acrylatesand methacrylates contain from 4 to 16 carbon atoms such as, forexample, 2-ethylhexyl acrylate and methyl methacrylates. It is alsopreferable that the monomers be used in a proportion such that the finalpolymer has a glass-transition temperature (Tg) greater than 21° C. andless than 95° C. The polymers preferably have a weight-average molecularweight of at least 100,000.

Preferably, the binding polymer comprises interpolymerized units derivedfrom 2-ethylhexyl acrylate. More preferably, the binding polymercomprises polymerized units comprising from 50 to 70 mole percent ofunits derived from styrene, methyl styrene, or combinations thereof;from 10 to 30 mole percent of units derived from 2-ethylhexyl acrylate;and from 10 to 30 mole percent of units derived from methyl acrylate,acrylonitrile, or combinations thereof.

Illustrative examples of suitable binding polymers include a copolymerwhose interpolymerized units are derived from about 49 mole percentstyrene, 11 mole percent alpha-methylstyrene, 22 mole percent2-ethylhexyl acrylate, and 18 mole percent methyl methacrylates with aTg of approximately 45° C. (available as Neocryl XA-6037 polymeremulsion from ICI Americas, Inc., Bridgewater, N.J.); a copolymer whoseinterpolymerized units are derived from about 51 mole percent styrene,12 mole percent .alpha.-methylstyrene, 17 mole percent 2-ethylhexylacrylate, and 19 mole percent methyl methacrylates with a Tg ofapproximately 44° C. (available as Joncryl 537 polymer emulsion fromS.C. Johnson & Sons, Racine, Wis.); and a terpolymer whoseinterpolymerized units are derived from about 54 mole percent styrene,23 mole percent 2-ethylhexyl acrylate, and 23 mole percent acrylonitrilewith a Tg of approximately 44° C. (available as Carboset™ XPD-1468polymer emulsion from B.F. Goodrich Co.). Preferably, the bindingpolymer is Joncryl™ 537.

As described above, the aluminum phosphate or polyphosphate madeaccording to various embodiments of the invention can be used toformulate latex paints as a pigment, alone or in combination withanother pigment.

Suitable additional hiding pigments include white opacifying hidingpigments and colored organic and inorganic pigments. Representativeexamples of suitable white opacifying hiding pigments include rutile andanatase titanium dioxides, lithopone, zinc sulfide, lead titanate,antimony oxide, zirconium oxide, barium sulfide, white lead, zinc oxide,leaded zinc oxide, and the like, and mixtures thereof. A preferred whiteorganic hiding pigment is rutile titanium dioxide. More preferred isrutile titanium dioxide having an average particle size between about0.2 to 0.4 microns. Examples of colored organic pigments are phthaloblue and hansa yellow. Examples of colored inorganic pigments are rediron oxide, brown oxide, ochres, and umbers.

Most known latex paints contain thickeners to modify the Theologicalproperties of the paint to ensure good spreading, handling, andapplication characteristics. Suitable thickeners include anon-cellulosic thickener (preferably, an associative thickener; morepreferably, a urethane associative thickener).

Associative thickeners such as, for example, hydrophobically modifiedalkali swellable acrylic copolymers and hydrophobically modifiedurethane copolymers generally impart more Newtonian rheology to emulsionpaints compared to conventional thickeners such as, for example,cellulosic thickeners. Representative examples of suitable associativethickeners include polyacrylic acids (available, for example, from Rohm& Haas Co., Philadelphia, Pa., as Acrysol RM-825 and QR-708 RheologyModifier) and activated attapulgite (available from Engelhard, Iselin,N.J. as Attagel 40).

Latex-paint films are formed by coalescence of the binding polymer toform a binding matrix at the ambient paint application temperature toform a hard, tack-free film. Coalescing solvents aid the coalescence ofthe film-forming binder by lowering the film-forming temperature. Thelatex paints preferably contain a coalescing solvent. Representativeexamples of suitable coalescing solvents include 2-phenoxyethanol,diethylene glycol butyl ether, dibutyl phthalate, diethylene glycol,2,2,4-trimethyl-1,1,3-pentanediol monoisobutyrate, and combinationsthereof. Preferably, the coalescing solvent is diethylene glycol butylether (butyl carbitol) (available from Sigma-Aldrich, Milwaukee, Wis.)or 2,2,4-trimethyl-1,1,3-pentanediol monoisobutyrate (available fromEastman Chemical Co., Kingsport, Tenn., as Texanol), or combinationsthereof.

Coalescing solvent is preferably utilized at a level between about 12 to60 grams (preferably about 40 grams) of coalescing solvent per liter oflatex paint or at about 20 to 30 weight percent based on the weight ofthe polymer solids in the paint.

The paints formulated in accordance with various embodiments of theinvention can further comprise conventional materials used in paintssuch as, for example, plasticizer, anti-foam agent, pigment extender, pHadjuster, tinting color, and biocide. Such typical ingredients arelisted, for example, in TECHNOLOGY OF PAINTS, VARNISHES AND LACQUERS,edited by C. R. Martens, R.E. Kreiger Publishing Co., p. 515 (1974).

Paints are commonly formulated with “functional extenders” to increasecoverage, reduce cost, achieve durability, alter appearance, controlrheology, and influence other desirable properties. Examples offunctional extenders include, for example, barium sulphate, calciumcarbonate, clay, gypsum, silica, and talc.

The most common functional extenders for interior flat paints are clays.Clays have a number of properties that make them desirable. Inexpensivecalcined clays, for example, are useful in controlling low-shearviscosity and have a large internal surface area, which contributes to“dry hide”. But, this surface area is also available to trap stains.

Because of their tendency to absorb stains, it is preferable thatcalcined clays are used in the paints of the invention only in the smallamounts required for rheology control, for example, typically as lessthan about half of the total extender pigment, or are not used at all.The preferred extenders for use in the paints of the invention arecalcium carbonates; most preferred are ultra-fine ground calciumcarbonates such as, for example, Opacimite (available from ECCInternational, Sylacauga, Ala.), Supermite. (available from Imerys,Roswell, Ga.), or others having particle size of approximately 1.0 to1.2 microns. Ultra-fine calcium carbonate help to space titanium dioxideoptimally for hide (see, for example, K. A. Haagenson, “The effect ofextender particle size on the hiding properties of an interior latexflat paint,” American Paint & Coatings Journal, Apr. 4, 1988, pp.89-94).

The latex paints formulated in accordance with various embodiments ofthe invention can be prepared utilizing conventional techniques. Forexample, some of the paint ingredients are generally blended togetherunder high shear to form a mixture commonly referred to as “the grind”by paint formulators. The consistency of this mixture is comparable tothat of mud, which is desirable in order to efficiently disperse theingredients with a high shear stirrer. During the preparation of thegrind, high shear energy is used to break apart agglomerated pigmentparticles.

The ingredients not included in the grind are commonly referred to as“the letdown.” The letdown is usually much less viscous than the grind,and is usually used to dilute the grind to obtain a final paint with theproper consistency. The final mixing of the grind with the letdown istypically carried out with low shear mixing.

Most polymer latexes are not shear stable, and therefore are not used asa component of the grind. Incorporation of shear unstable latexes in thegrind can result in coagulation of the latex, yielding a lumpy paintwith no, or little, film-forming capability. Consequently, paints aregenerally prepared by adding the latex polymer in the letdown. However,the some paints formulated in accordance with various embodiments of theinvention contain latex polymers that are generally shear stable.Therefore, the latex paints can be prepared by incorporating some or allof the latex polymer into the grind. Preferably, at least some of thelatex polymer is put in the grind.

Two examples of possible forms of the process are described below.Again, one of skill in the art will recognize variants that may beutilized in performing the novel process described herein. The followingexamples are presented to exemplify embodiments of the invention. Allnumerical values are approximate. When numerical ranges are given, itshould be understood that embodiments outside the stated ranges maystill fall within the scope of the invention. Specific details describedin each example should not be construed as necessary features of theinvention.

Example No. 1

In this example, 535.0 kg of aluminum phosphate was prepared. The wetproduct was dried in a “turbo-dryer” and presented characteristics ofhollow particles with 15% humidity and P:Al (phosphorus:aluminum) ratioof 1:1.50.

940.0 kg of fertilizer phosphoric acid containing 55.0% of P₂O₅ wasprepared. In the initial preparation phase, the acid discoloration wascarried out, which lasted approximately thirty minutes, at a temperatureof 85° C. For this phase, a solution with 8.70 kg of hydrogen peroxidecontaining around 50% of H₂O₂ was added to the acid. Then, the acid wasdiluted with 975.0 kg of process water, cooled to a temperature of 40°C. and then stored at the concentration of 27.0% of P₂O₅.

The aluminum source employed in this application was a commercialaluminum sulfate solution containing 28% of Al₂O₃. The solution wasfiltered and diluted with process water. Specifically, 884.30 kg ofaluminum sulfate solution and 1,776.31 kg of process water was combinedto create a solution of approximately 9.30% Al₂O₃.

This particular experiment used as a neutralizing reagent a dilutedsolution of commercial sodium hydroxide containing 20.0% of NaOH.Specifically, 974.0 kg of sodium hydroxide solution with 50% of NaOH and1,461.0 kg of process water were mixed. The final mixture was cooled to40° C.

The three reagents were mixed simultaneously, for approximately 30minutes, in a reactor with 7,500 liters. During the addition of thereagents in the reactor, the mixture temperature was kept in the 40° C.to 45° C. range, the pH was controlled to stay in a range of 4.0 to 4.5.At the end of the addition of reagents, the mixture was kept sloshingfor approximately 15 minutes. The pH at this point was controlled atapproximately 5.0 with the addition of a sodium hydroxide solutioncontaining 5.0% of NaOH. The resulting suspension was approximately7,000 kg with a density of 1.15 g/cm³, presented 6.5% of solids, whichrepresent around 455.0 kg of precipitate.

Then, the suspension was filtered in a press-filter resulting in 1,300kg of wet cake and 5,700 kg of filtrate. The filtrate consistedprimarily of a sodium sulfate solution (Na₂SO₄). The cake consisted ofapproximately 35% solids. The cake was washed, directly in the pressfilter, with 3,860 liters of process water, at room temperature, beingkept at a washing ratio of approximately 8.5 cm³ of the washing solutionper ton of dry cake. The filtrate generated in the washing of the cakewas stored for optional future use or for effluent treatment. The cakeextracted from the filter, around 1,300 kg, was then transferred to adisperser (of approximately 1,000 liters) through a peristaltic pump.The dispersed solution, containing approximately 35% of solids, had adensity of 1.33 g/cm³ and viscosity of 17,400 cP.

The dispersed aluminum phosphate suspension, with approximately 35% ofsolids, was then pumped to a turbo-drier. The product was heated,through a hot air stream, at a temperature of 135° C. Approximately535.0 kg of aluminum orthophosphate with 15% of humidity was produced.The final product was micronized and its granulometry was kept below the400 mesh. The final analysis of the dry product presented the followingresults: the phosphorus content in the product was approximately 15.0%;the aluminum content was approximately 8.7%; the pH was approximately7.0; the water content was approximately 15%; specific density of 2.20g/cm³, and average diameter of particles from 5 to 10 um.

Example No. 2

From the results of Example No. 1, around 200 kg of dried and micronizedaluminum phosphate was used. The sample was used for the manufacturingof a home paint sample. Initially, 900 liters of opaque white acrylicpaint was prepared. Such paint was applied and the performance wasevaluated in comparison with one of a commercially available paint. Thebasic composition of the paint based on an original formulationcontaining around 18% of titanium dioxide was as follows: aluminumphosphate was approximately 14.20%; titanium oxide was approximately8.34%; kaolin was approximately 7.10%; algamatolite was approximately10.36%; diatomite was approximately 0.84%; acrylic resin wasapproximately 12.25%, and PVC was approximately 47.45%. Thecharacteristics of the paint prepared with aluminum phosphate, after theapplication of it in painting, was the as follows: a) wet coveragesimilar to the reference paint coverage; b) dry coverage was better thanthe coverage with the reference paint; and c) resistance tests after sixmonths of home painting provided excellent results. Finally, it was seenthat the opaque acrylic paint soluble in water with aluminum phosphate,prepared in Example No. 2, kept all the characteristics of commerciallyavailable paints with yield of 50 m²/3.6 liters on the surface preparedwith filler.

Typical chemical composition data of the aluminum phosphate product isin Table 1. These results demonstrate that the invention describedherein is a hydrous, non-crystalline and neutral aluminum phosphate madeout of nanosized particles. In addition, the average aggregate, andswollen, particle size (in the slurry) is in the 200-1500 nm range, asdetermined by dynamic light scattering. More preferably, the averageaggregate, and swollen, particle size (in the slurry) is in the 400-700nm range. Individual particle sizes, however, may have a radius as smallas 5 to 80 nm, as determined by electron microscopy. More preferably,the individual particle sizes may have a radius as small as 10 to 40 nm.

TABLE 1 Chemical Compositions of Various Grades of Novel Product AsDetermined by X-Ray Fluorescence Using Fundamental Parameters Grade P AlS Si Fe Ca 1 1 0.8 nil 0.067 0.0006 0.0005 2 1 0.82 nil 0.049 0.00050.0014 3 1 0.769 0.026 0.058 0.0007 0.0012 4 1 1.26 0.54  0.04 0.019 nil

As mentioned, a basic titanium dioxide water-based paint is made out ofa suitable latex dispersion and pigment particles. The latex particlesare responsible for making a coalesced film filled with the pigmentedparticles, and are responsible for the film hiding power. Many additivesare also used, such as: inorganic fillers, which decrease therequirements of resin and pigment; coalescing agents, that improve resinfilm formation; dispersants and rheological modifiers, that preventpigment and filler caking and thus improve the paint shelf-life togetherwith the rheological paint properties.

In a typical paint dry film, the pigment and filler particles aredispersed in the resin film. The hiding power is largely dependent onthe particle refractive indices and sizes. As mentioned titanium dioxideis currently the standard white pigment because of its large refractiveindex and of the absence of light absorption in the visible region. Adry film of a paint formulated with the novel aluminum phosphate in someembodiments has several differences from the typical paint dry film.First, the film with the aluminum phosphate is not just a resin film. Itis rather formed by enmeshed resin and aluminum phosphate. It is thus ananocomposite film that combines two interpenetrating phases withdifferent properties to achieve synergistic benefits, concerning filmmechanical properties and resistance to water and to other aggressiveagents. Second, good film hiding power is obtained at lower titaniumdioxide contents, because the film contains a large amount of closedpores that scatter light. Moreover, if a titanium dioxide particle isadjacent to one of these voids, it will scatter much more than if it isfully surrounded by resin, due to the larger refractive index gradient.This creates a synergism between the novel aluminum phosphate andtitanium dioxide, as far as the hiding power is concerned.

In tests comparing a standard paint dry film to a film with aluminumphosphate, a standard market formulation of a semi-matt acrylic paintwas chosen and titanium dioxide was progressively replaced by the novelaluminum phosphate product described herein. Water content and otherpaint components were adjusted as required. Several of the modificationsin the formula in this embodiment are related to a decreased use ofthickener/rheology modifier, dispersant, acrylic resin and coalescingagent. Table 2 describes an example of one of the formulas used in thisexperiment, together with the corresponding formula for the novelaluminum phosphate.

TABLE 2 A standard paint formula currently used in the market and thecorresponding formula using the aluminum phosphate. The amounts aregiven in grams. Formula prepared Standard Formula using novel slurryWater 839.79 361.86 Propyleneglycol 30.00 30.00 Thickener/rheologymodifier 84.00 4.50 Antifoaming agent 0.60 1.17 Sodium tetrapyrophosfate0.87 9.00 Anti-oxidant 0.87 0.90 Dispersant 20.94 11.00 Ammine 5.00 AFEanionic 7.86 7.86 Bactericide 4.50 4.50 Fungicide 4.50 4.50 Ammoniumhydroxide 25% 7.11 15.00 Titanium dioxide 534.00 267.00 Kaolin # 325169.50 169.50 CaCO₃ nat. Micronized 161.28 161.28 Dolomite # 325 300.00300.00 Aluminium silicate # 1000 60.18 60.18 Aluminum phosphate slurry763.00 0.35 Acrylic resin 735.00 591.00 Antifoaming/mineral spirit 9.006.00 Coalescing agent 60.00 43.47 Total (grams) 3030.00 2816.72

In the formula above, a replacement of 50% TiO₂ (on a weight basis) wasachieved, keeping the opacity and whiteness conditions of the dry film.In addition, the other properties of the novel product as a rheologicalmodifier and also as a film structuring agent were explored. Comparisonbetween the two formulas above shows that the pigments made according toembodiments of the invention will lead to additional cost reductionbeyond that derived from the replacement of titanium dioxide pigment.Moreover, such gains may be obtained while producing a betterperformance in the applied paint film.

It can be observed from the foregoing description of differentembodiments of the invention that the novel product and process differsfrom existing aluminum phosphates or polyphosphates in several aspects.For example, as its stoichiometry is not definite, various formulationsof the invention can be prepared by changing the fabrication process andthus the final product composition. Because the invention is made undercontrolled pH levels, it is nearly neutral thus avoiding environmentaland toxicological problems.

In addition, the invention may also be free from corrosion problemsassociated with some aluminum phosphates found in the market and used inthe transformation of iron oxides into iron phosphate. In addition, thenon-stoichiometry together with the relative non-crystallinity (both inslurry and powder form) and the carefully controlled water content ofthe dry powder allow for easy swelling control that is beneficial forits performance. The nanosized particles are easily dispersed and theyare stable towards settling, which allow uniform paint dispersions.Also, the nanoparticles can be strongly compatible with latex particles,by the mechanisms of capillary adhesion (in the dispersion drying stage)followed by ion-cluster mediated electrostatic adhesion (in the dryfilm)—bicontinuous networks may be formed, in many cases. Finally, thenovel product is also strongly compatible with many other particulatesolids commonly used as paint fillers, such as the various silicates,carbonates and oxides found in formulated water-based dispersions, whichmay contribute to the cohesion and strength of the paint dry film.

Thus, the invention described herein uses a different raw material thatoffers alternate benefits, making the process more economical andoffering surprising results. Disclosed herein are the purification,discoloration, and purification of a phosphoric acid, broadly availablein the fertilizer industry. Phosphoric acid is generally available at aprice which is a fraction of the price of the phosphates ormetaphosphates previously used. As the phosphoric is the raw materialthat typically has the highest price used in the manufacturing ofaluminum phosphates pigment manufacturing, the use of an acid degreeallows an important reduction in the manufacturing costs of aluminumphosphates. Such a process makes the broad adoption of these pigmentsfeasible. In addition, certain features of the invention describedherein present new ways to use the aluminum phosphates, such as indispersion or in wet powder. These new methods allow importanttechnological gains. For example, the novel methods and products preventproblems of particle aggregation, which damage the performance of thepigment and reduce its coverage power. In addition, the novel method andproduct eliminate problems of particles dispersion in latex particlesused in the manufacturing of paints based on water, facilitating theusage processes of aluminum phosphate in home paints. Further, the novelprocesses and products do not require exhaustive drying steps of thephosphate, which increase the complexity and cost of manufacturing.

Another beneficial aspect of the novel process described herein is thatit may be considered a “green chemistry” zero-effluent product, in thatit is made under mild temperature and pressure conditions that do notcreate any environmental problems during the fabrication process. Due toits chemical nature, the residues created by the described novel processmay be safely discarded in the environment as a fertilizer component. Itis produced as slurry as well as a dry powder. In both cases it iseasily dispersed in water, forming stable dispersions that have stableTheological properties.

As demonstrated above, embodiments of the invention provide a novelmethod of making amorphous aluminum phosphate. While the invention hasbeen described with respect to a limited number of embodiments, thespecific features of one embodiment should not be attributed to otherembodiments of the invention. No single embodiment is representative ofall aspects of the invention. In some embodiments, the compositions ormethods may include numerous compounds or steps not mentioned herein. Inother embodiments, the compositions or methods do not include, or aresubstantially free of, any compounds or steps not enumerated herein.Variations and modifications from the described embodiments exist. Themethod of making the resins is described as comprising a number of actsor steps. These steps or acts may be practiced in any sequence or orderunless otherwise indicated. Finally, any number disclosed herein shouldbe construed to mean approximate, regardless of whether the word “about”or “approximately” is used in describing the number. The appended claimsintend to cover all those modifications and variations as falling withinthe scope of the invention.

1. A method of making a coating composition comprising amorphousaluminum phosphate comprising the steps of: combining phosphoric acidwith aluminum sulfate and an alkaline solution to form a mixture;reacting the mixture to form an amorphous aluminum phosphateprecipitate; drying the precipitate at a temperature less than about130° C.; and adding the amorphous aluminum phosphate to a bindingpolymer to form the coating composition.
 2. The method as recited inclaim 1 wherein dried precipitate comprises one to four closed voids perparticles.
 3. The method as recited in claim 1 wherein the alkalinesolution is sodium hydroxide.
 4. The method as recited in claim 1wherein the dried precipitate is substantially free of open pores. 5.The method as recited in claim 1 wherein the dried precipitate comprisesa macropore volume that is substantially less than 0.1 cc/gram.
 6. Themethod as recited in claim 1 wherein during the step of combining, thephosphoric acid, aluminum sulfate, and alkaline solution are combinedsimultaneously.
 7. The method as recited in claim 1 wherein the step ofreacting takes place for a predetermined amount of time.
 8. The methodas recited in claim 1 wherein the step of reacting takes place forapproximately 30 minutes.
 9. The method as recited in claim 1 whereinthe amorphous aluminum phosphate has a phosphorous to aluminum moleratio of greater than about 0.8.
 10. The method as recited in claim 1wherein after the step of combining, adding further sodium hydroxide tothe mixture.
 11. The method as recited in claim 1 wherein the coatingcomposition is a water-borne latex based composition.
 12. The method asrecited in claim 1 wherein the coating composition further comprises anopacifying pigment.
 13. The method as recited in claim 1 wherein beforethe step of combining, treating the phosphoric acid with hydrogenperoxide at elevated temperature.
 14. The method as recited in claim 1wherein when in powder form the amorphous aluminum phosphate has anaverage individual particle radius size of between 20 and 80 nanometers.15. A method of making a coating composition comprising an amorphousaluminum phosphate pigment comprising the steps of: combining phosphoricacid with aluminum sulfate and sodium hydroxide to form a mixture;reacting the mixture to form an amorphous aluminum phosphateprecipitate, wherein the amorphous aluminum phosphate has a phosphorousto aluminum mole ratio of greater than about 0.8; and drying theprecipitate at a temperature less than about 130° C., wherein the driedprecipitate is substantially free of open pores; and adding theamorphous aluminum phosphate to a binding polymer to form the coatingcomposition.
 16. The method as recited in claim 15 wherein the driedprecipitate when in a powder form comprises one to four closed voids perparticle.
 17. The method as recited in claim 15 wherein after the stepof reacting, washing the amorphous aluminum phosphate.
 18. The method asrecited in claim 15 wherein after the step of drying, the amorphousaluminum phosphate has a macropore volume of substantially less than 0.1cc/gram.
 19. The method as recited in claim 15 comprising combining thephosphoric acid, aluminum sulfate, and sodium hydroxide simultaneously.20. The method as recited in claim 15 wherein during the step of adding,the amorphous aluminum phosphate is provided in the form of a slurry.21. The method as recited in claim 20 wherein the concentration ofsolids in the slurry is in the range of from about 10 to 55 percent. 22.The method as recited in claim 15 wherein the coating compositionadditionally comprises titanium dioxide.
 23. The method as recited inclaim 15 wherein when in powder form the amorphous aluminum phosphatehas an average individual particle radius size of between 20 and 80nanometers.
 24. The method as recited in claim 15 wherein the coatingcomposition is a water-borne latex composition.
 25. The method asrecited in claim 15 wherein the amorphous aluminum phosphate has a bulkdensity of less than 2.3 grams/cc.
 26. The method as recited in claim 15wherein the step of reacting takes place for approximately 30 minutes.27. A method of making a coating composition comprising an amorphousaluminum phosphate opacifying pigment comprising the steps of: combiningphosphoric acid with aluminum sulfate and sodium hydroxide to form amixture; reacting the mixture to form an amorphous aluminum phosphatesuspension filtrating and washing the suspension into a cake; forming adispersion of the washed cake; drying the cake to form amorphousaluminum phosphate particles; and adding the amorphous aluminumphosphate to a binding polymer to form the coating composition.
 28. Themethod as recited in claim 27 wherein after the step of drying, theamorphous aluminum phosphate particles have one to four closed voids perparticle.
 29. The method as recited in claim 27 wherein the step ofdrying is performed at less than about 130° C.
 30. The method as recitedin claim 27 wherein after the step of drying, the amorphous aluminumphosphate has a macropore volume of substantially less than 0.1 cc/gram.31. The method as recited in claim 27 wherein after the step of drying,the amorphous aluminum phosphate is substantially free of open pores.32. The method as recited in claim 27 wherein the amorphous aluminumphosphate has a phosphorous to aluminum mole ratio of greater than 0.8.33. The method as recited in claim 27 wherein the amorphous aluminumphosphate has a bulk density of less than 2.3 grams/cc.
 34. The methodas recited in claim 27 comprising combining the phosphoric acid,aluminum sulfate, and sodium hydroxide simultaneously.
 35. The method asrecited in claim 27 wherein when in powder form the amorphous aluminumphosphate has an average individual particle radius size of between 20and 80 nanometers.
 36. The method as recited in claim 27 wherein thecoating composition additionally comprises another type of opacifyingpigment.
 37. The method as recited in claim 27 wherein after the step ofcombining, adding further sodium hydroxide to the mixture.
 38. A methodof making a coating composition comprising an amorphous aluminumphosphate opacifying pigment comprising the steps of: simultaneouslycombining phosphoric acid with aluminum sulfate and an alkaline solutionto form a mixture; reacting the mixture to form an amorphous aluminumphosphate precipitate, wherein the amorphous aluminum phosphate has aphosphorous to aluminum mole ratio of greater than 0.8; and drying theprecipitate at a temperature less than about 130° C., wherein when in apowder form the amorphous aluminum phosphate has one to four closedvoids per particle and has a macropore volume of substantially less than0.1 cc/gram, wherein the amorphous aluminum phosphate has an averageindividual particle radius size of between 20 and 80 nanometers, andwherein the amorphous aluminum phosphate has a bulk density of less than2.3 grams/cc; and adding the amorphous aluminum phosphate to a bindingpolymer to form the coating composition, and wherein the coatingcomposition comprises a water-borne latex.
 39. The method as recited inclaim 38 wherein the step of reacting takes place for approximately 30minutes.
 40. The method as recited in claim 38 wherein the alkalinesolution is sodium hydroxide.